This invention concerns the art of manganese nodule processing. More specifically, the invention concerns a method for removing finely divided solids from water used in processing manganese nodules.
Manganese nodules are found at various locations on the ocean floor. The nodules have a concentric layer structure, and include many different minerals such as hydrous manganese and iron oxides and clays. The nodules contain metals such as copper, nickel, cobalt, molybdenum, manganese and iron. They also include a large variety of other minerals and inclusions. Several methods have been proposed for recovering the nodules for their metals (Cu, Co, Ni and Mn) values. Typically, proposed nodule mining systems make use of mechanical scoops or suction devices to harvest the nodules and some sediment. [The nodules can be concentrated and separated from the very fine (.perspectiveto.1 micron) sediment in a simple hydraulic device.] The nodules are then transported to the surface of the ocean, usually as a slurry in sea water. The sea water is decanted and returned to the ocean. The nodules are unavoidably abraded and fractured to some extent during transport to the water surface. Although most of the solids brought to the surface in the nodule slurry can be settled out of the slurry prior to discharging the sea water, a residue of finely divided, dispersed solids is present in the water and is not easily settled. This finely divided solids residue presents a potential contaminant when the water is discharged. In the case of a large scale nodule mining operation, the amount of finely divided solids potentially to be discharged into the ocean from the nodule recovery operation could result in a water pollution problem. The present invention is concerned, in part, with preventing ocean water pollution from finely divided solids as a result of contaminated sea water discharge in a nodule recovery operation. Aqueous liquids containing finely divided nodule solids are also generated in various operations used for recovering valuable metals such as cobalt, nickel and copper from manganese nodules. The present invention may also be advantageously employed in removing finely divided solids from such nodule processing streams. A variety of processing systems have been suggested in the prior art for removing the valuable metals from the nodules.
High gradient magnetic separation is used commercially to separate discolorants from clay to brighten the clay. Finely divided clay is slurried in water and is passed through a cartridge containing a ferromagnetic matrix. The matrix is maintained in a strong magnetic field. A magnetically susceptible fraction consisting of ferromagnetic and paramagnetic particles, termed "mags", is held onto the matrix, while diamagnetic clay particles, termed "tails", pass through the matrix and out of the filtering cartridge. Beneficiation of clay, calcium carbonate, and the like by magnetic separation is discussed in U.S. Pat. No. 3,471,011, No. 3,482,685, No. 3,980,240 and No. 3,985,646. Types of high gradient magnetic separation apparatus are discussed in U.S. Pat. No. 3,627,678, and No. 3,676,337. Magnetic separation has also been used commercially for beneficiating magnetic iron ores. Such a system is discussed in U.S. Pat. No. 3,608,718. High gradient magnetic separation has been proposed as a method for removing oil and suspended solids from waste water streams. Magnetically susceptible pollutants can be removed directly, while non-magnetic pollutants can be removed by seeding the waste water with magnetite and agglomerating the pollutants prior to magnetic treatment. See, for example, IEEE Transactions On Magnetics, Vol. Mag-14, No. 5, September 1978, pages 491-493.